The present invention relates generally to adhesive application systems and, more particularly, to systems designed to be used with polyurethane (PUR) and other adhesives that cure by reacting with moisture in ambient air.
Reactive hot melt adhesive coating machines are commonly used to spray a reactive hot melt adhesive onto an applied object with the use of one or more nozzles. The reactive hot melt adhesive is supplied from an adhesive supply unit having an adhesive supply hopper or storage tank which stores the reactive hot melt adhesive in a molten condition. The molten material is fed through an adhesive heating passage with appropriately pressurized air. An exemplary system is disclosed, for example, in U.S. patent application Ser. No. 09/179,964, filed Oct. 28, 1998, entitled xe2x80x9cReactive Hot Melt Adhesive Coating Machinexe2x80x9d, assigned to Illinois Tool Works, Inc., Chicago, Ill., the assignee of the present invention. The disclosure of the ""964 application is incorporated by reference herein in its entirety.
The adhesive supply unit such as the type described above is also designed to be used with polyurethane (PUR) adhesives. Polyurethane adhesives produce an extremely strong bond and they may be used for structural purposes or for laminates, carpet bonding, etc. They contain no solvents, which makes them environmentally desirable. However, PUR adhesives react to moisture and typically must be melted at temperatures below 300xc2x0 F. (149xc2x0 C.), although the actual melting temperature may vary depending on adhesive manufacturer. To put PUR adhesives to practical use, however, all moisture must be removed from the air within the supply hopper of the adhesive supply unit. To remove moisture, one adhesive supply unit that is presently sold by the assignee of the present invention in Japan solves these problems by removing moisture with a sequenced drying and vacuum purge cycle after the adhesive is introduced into the hopper tank. Moisture removal is achieved by supplying super dry air through a series of dryers or filters designed to remove the moisture.
One of the problems with the above commercial system is that the air control system for removing moisture is mounted on a separate cart that is not a part of the machine per se. In addition to bulkiness and occupying space, lengthy air lines are necessary to pneumatically interconnect the air control system with the machine hopper. In addition to requiring additional space and increasing the number of external parts surrounding the machine, these lengthy air lines increase the valve response times and lengthen the process times for removing moisture.
Other potential drawbacks with the above commercial device exist. For example, the hopper lid used to seal off the adhesive in the hopper from the ambient environment did not always close properly which is critical in order to remove moisture within a pre-determined short amount of time before the PUR adhesive cures. Yet another drawback associated with the above commercial machine was that the actuation of the moisture purging cycle was manually controlled and the time sequence for the purge was manually inputted. One problem with this approach is that the time involved varies as a function of the amount of adhesive in the hopper.
It is accordingly an object of the present invention to integrate the air control components directly onto the adhesive supply machine.
Another object is to minimize the space necessary for the adhesive supply machine and associated air control to occupy on a production floor.
Still a further object of the invention is to incorporate a heavy duty hopper lid and top closure that positively clamps onto the hopper to assure a moisture tight closure.
Yet a further object is to automate the electronic cycling of the air control system so that the cycle automatically starts to remove moisture from the hopper once the lid is closed shut.
A further object is to automatically control the pressure inside the hopper while compensating for the amount of adhesive in the hopper.
The adhesive supply machine for supplying polyurethane (PUR) and other adhesives is comprised of a melter body including a hopper having an interior storage region for receiving the PUR adhesive in solid form, and at least one heating element disposed within the hopper for melting the adhesive. The hopper includes an open top that is selectively opened and closed with a lid. When closed, a control system associated with the machine automatically actuates an air control that removes moisture from the air within the hopper in a dryer/purge cycle after the adhesive is introduced. The purge cycle is repetitive for a predetermined number of times in order to replace the moisture-laden air with super dry air while providing a vacuum within the hopper at a predetermined vacuum pressure.
In accordance with one unique feature of the present invention, a unique clamping arrangement is provided to assure positive clamping of a lid base to the hopper to prevent a breach of the seal and the undesirable introduction of ambient moisture laden air into the hopper that will prematurely cause the molten polyurethane therein to cure. To facilitate reliable clamping, a unique clamping bar arrangement is used to secure the lid base directly to the hopper body. This is achieved in the preferred embodiment by clamping the bars directly to the open mouth of the hopper and in turn securing the lid base to the clamping bars with screws.
Another improvement feature of this invention is the integration of an assortment of dryers and filters in an air drying circuit that alternates with a vacuum purge cycle achieved with a vacuum generator to both dry the air within the hopper to within an acceptable range while providing predetermined desired vacuum pressure conditions. The purge cycle is automatically controlled by the control system and is automatically initiated once the lid is latched closed as detected by a sensor associated with a lid position switch. The sensor is preferably an optical sensor, instead of a mechanical sensor, which results in reduced weight and costs.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications and various obvious respects, all without departing from the invention. Accordingly, the description is to be regarded as illustrated in nature, and not as restricted.